1. Field of Invention
The present invention relates generally to semiconductor processing equipment. More particularly, the present invention relates to a scanning stage apparatus which may be efficiently implemented for use in an electron beam projection system.
2. Description of the Related Art
Lithography processes, e.g., photo-lithography processes, are integral to the fabrication of wafers and, hence, semiconductor chips. Conventional systems used for lithography include optical lithography systems and electron beam projection systems. Many optical lithography systems and electron beam projection systems may use a direct writing process to xe2x80x9cwritexe2x80x9d on wafers. However, direct writing processes are often relatively slow, as will be appreciated by those skilled in the art.
In order to increase the speed at which wafers may be written to, electron beam projection systems, as well as optical lithography systems, may project beams of finite area through patterns. The patterns are generally resident on a reticle, which effectively serves as a mask or a negative for a wafer. For an electron beam projection system, a relatively broad beam of electrons may be collimated and provided to a reticle, which may be a silicon wafer, e.g., a wafer that is suitable for scattering with angular limitation projection electron beam lithography or a stencil-type wafer. Typically, rather than absorbing the beam, the pattern deflects portions of the beam in order to prevent electrons from being ultimately focused onto a wafer.
FIG. 1a is a diagrammatic representation of one standard configuration of a lens system of an electron beam projection system. In general, a lens system 104 includes an illumination lens 108 and a projection lens 124. An electron beam is arranged to pass through illumination lens 108, to a reticle 112 that is held by a reticle stage 116 in a vacuum chamber 120. As an electron beam passes through reticle 112, portions of the electron beam are allowed to pass through reticle 112, while other portions of the electron beam may be scattered to prevent those portions from being focused onto a wafer 128 that is held, e.g., by a stage (not shown), in a wafer chamber 130, i.e., a vacuum chamber. In other words, reticle 112 acts as a mask to effectively mask out part of an electron beam. Projection lens 124 is arranged to project the pattern of electrons, i.e., the pattern of electrons which are not masked out by reticle 112, onto wafer 128.
Stages, such as reticle stage 116 or a wafer stage, are often used to facilitate a lithography process. The use of reticle stage 116, for example, enables reticle 112 to be readily scanned over a surface of wafer 128 to enable a pattern of electrons to be projected onto different portions of wafer 128. The design of a stage such as reticle stage 116 for use in an electron beam projection system may be complicated, as an electron beam projection system generally must not include moving magnets or metals which alter the magnetic field associated with the electron beam projection system and, hence, the electron beam.
Although separate vacuum chambers may be used to house a reticle and a wafer, an entire lens system may generally be housed in a single vacuum chamber. FIG. 1b is a diagrammatic representation of a standard lens system of an electron beam projection system which is contained within a vacuum chamber. Like lens system 104 of FIG. 1a, a lens system 154 includes an illumination lens 158 and a projection lens 174. An electron beam is arranged to pass through illumination lens 158. The electron beam then passes from illumination lens 158 to a reticle 162 that masks out part of the electron beam. Reticle 162 is generally positioned on a reticle stage 170 that allows reticle 162 to be scanned. After passing through reticle 162, portions of the electron beam which are not masked out by the reticle then pass through projection lens 174 and onto wafer 178. As shown, illumination lens 158, reticle 162, reticle stage 170, projection lens 174, and wafer 178 are all contained within a vacuum chamber 180.
Electron beam projection systems are often used in lieu of optical systems because a lens system associated with an electron beam projection system may dynamically move a projection image to follow a stage, which is generally not possible with an optical system, as will be appreciated by those skilled in the art. In addition, electron beam lens systems typically correct for relatively small errors in relative stage positions, whereas optical systems generally do not. However, electron beam projection systems often have specific requirements which are not requirements for typical optical lithography systems. By way of example, an electron beam projection system generally must operate in a high vacuum environment. Maintaining a high vacuum environment may be expensive, as any gas leakage into the vacuum environment must be corrected as the gas leakage typically compromises the vacuum level.
It is often desirable to have moving parts associated with an electron beam projection system. For example, a wafer may be placed on a wafer stage which enables the wafer to be positioned beneath a projection column as appropriate. Similarly, a reticle placed on a reticle stage enables the position of the reticle with respect to a wafer to be readily adjusted. However, moving parts within a vacuum may cause problems with electron beams as linear motors and magnetic elements may interfere with magnetic fields. An electron beam projection system may not include moving magnets, as moving magnets cause the magnetic field associated with the electron beam projection system to change. Further, an electron beam projection system also may not having moving iron structures, due to the fact that moving iron dynamically alters the static magnetic fields around an electron beam lens, as will be appreciated by those skilled in the art.
Many scanning stage devices which are suitable for use in a high vacuum environment are relatively large, e.g., have a relatively large moving mass. The size of the scanning stage devices is due, at least in part to, arranging the stage device such that linear motors or magnetic elements do not significantly affect an electron beam. As will be appreciated by those skilled in the art, the larger a mass is, the larger the power requirements are for moving the mass. Many conventional stage devices also leak a significant amount of gas into a vacuum chamber, as air bearings are often used to support and guide portions of stages within a vacuum, and many standard air bearings leak. Maintaining the vacuum level in a vacuum chamber to accommodate gas leakage is often difficult or impractical.
Therefore, what is needed is a method and an apparatus for enabling reticles to be scanned efficiently within an electron beam projection system. That is, what is desired is a vacuum compatible stage which is relatively compact, efficient, and suitable for use in a relatively high vacuum environment.
The present invention relates to an air bearing stage device for use in a vacuum environment which maintains linear motors and magnetic elements outside of a vacuum chamber. According to one aspect of the present invention, a scanning stage apparatus includes a table that is positioned in a system vacuum chamber and a first rod that carries the table. The apparatus also includes first and second plates that support the first rod. The first plate includes an air bearing surface that is arranged to be held against the first side of a first wall by a first vacuum force. A first drive mechanism drives the first plate to move the first rod in a first direction, and also drives the second plate to move the first rod in the first direction, while a second drive mechanism which includes a second rod and a first linear motor causes the second rod to move the first rod in a second direction. In one embodiment, the first wall is an exterior wall of the system vacuum chamber within which a vacuum level is maintained.
In another embodiment, the scanning stage apparatus also includes a first sleeve and a second sleeve. The first sleeve supports the first rod through the first sleeve such that when the first drive mechanism drives the first plate to move the first rod in the first direction, the first drive mechanism drives the first plate such that the first plate moves the first sleeve and the first rod. The second sleeve also supports the first rod through the second sleeve such that when the first drive mechanism drives the second plate to move the first rod in the first direction, the first drive mechanism drives the second plate such that the second plate moves the second sleeve and the first rod. In such an embodiment, the first sleeve may be in contact with the first plate through a first flexure bearing and the second sleeve may be in contact with the second plate through a second flexure bearing.
A scanning stage apparatus of the present invention reduces the amount of gas leakage into a system vacuum chamber, and also maintains actuators and magnetic elements outside of the system vacuum chamber. Hence, contamination and magnetic interference within the system vacuum chamber may be reduced. In addition, the mass of a moving portion of a stage may be reduced through the use of hollow rods to carry a table, as well as the positioning of motors off of the hollow rods. Maintaining actuators, e.g., linear motors, in an air environment as opposed to a vacuum environment also allows for easier access to the actuators, e.g., for maintenance purposes. Therefore, the scanning stage apparatus may operate more efficiently and more precisely.
According to another aspect of the present invention, a stage device that is arranged to scan a reticle in a vacuum environment includes a rod and a table that accommodates the reticle and is coupled to the first end of the rod. First and second plates support the rod. At least the first plate includes an air bearing surface that is at least partially held against an exterior wall of a system vacuum chamber by a first vacuum force. A first drive arrangement drives the first plate and the second plate in a first direction and, hence, drives the rod in the first direction. A second drive arrangement that is coupled to the first rod drives the first rod in a second direction. Finally, a third drive arrangement that is substantially coupled to the second drive arrangement drives the first rod, the first plate, and the second plate in a third direction. The third drive arrangement, the second drive arrangement, the first drive arrangement, the first plate, and the second plate are substantially external to the system chamber.
In one embodiment, the second drive arrangement is coupled to the second end of the first rod and the system chamber contains a vacuum. In such an embodiment, a force counteractor counteracts atmospheric pressure forces on the first rod that have the tendency to pull or push the first rod into the system chamber. The force counteractor may include a spring arrangement which applies a force to the first coil to counteract the atmospheric pressure forces on the first rod.
In another embodiment, the second drive arrangement is coupled to the first rod between the first end and a second end of the rod, and the system chamber contains a first vacuum. In such an embodiment, a dummy chamber which contains a second vacuum accommodates the second end of the first rod therein. The dummy chamber often includes an exterior surface, and the second plate often includes an air bearing surface that is arranged to at be held against the exterior surface of the dummy chamber by a second vacuum force.
According to still another aspect of the present invention, a scanning stage apparatus includes a system chamber which has a vacuum level and an external surface, as well as a table positioned within the system chamber and a rod which carries the table. A first plate is arranged to support the rod substantially outside of the system chamber, and includes a first surface that is substantially held against the external surface of the system chamber by a first vacuum force. A second plate is also arranged to support the rod substantially outside of the system chamber. A first actuator arrangement drives the first plate and the second plate along a first axis such that the rod is also driven along the first axis. A second actuator arrangement drives the first plate and the second plate along a second axis, and effectively drives the rod along the second axis.
In one embodiment, the first plate supports the rod through a first sleeve and the second plate supports the rod through a second sleeve. In such an embodiment, the first plate and the first sleeve are flexually attached to enable the rod to rotate about the first axis and about the second axis. The flexural attachment may be accomplished through the use of a flexure bearing.
In another embodiment, the scanning stage apparatus includes a dummy chamber that is arranged to maintain a vacuum level therein. The rod is coupled to the table at a first end of the rod and a second end of the rod is positioned within the dummy chamber, whereby positioning the second end of the rod within the dummy chamber counteracts at least some of the atmospheric pressure forces associated with the rod. In such an embodiment, the dummy chamber may include an external surface, and the second plate may include a first surface that is substantially held against the external surface of the dummy chamber by a second vacuum force.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.